Process of making thiourea



PRocEss 0F 'MAKING www@ Y @mgm-aa Filed 'June "zu, 1958 Patented Dec. 16, 1941 1 2,266,221 UNITED STATES PATENTVOFFICE 2.266.221 Y Lrlaooizss oF MAKING '.rm'ouam wuuam Bruce Ieren, clyae i1r. Mathis, and Eugene J. Gatchell, Bartlesville, Okla., assignors to Phillips Petroleum Company, va. corporation of Delaware 1940, Serial No..341,562`

2 Claims..

The invention relates-tothe process of using the hydrogen sulfide and objectionable sulphur compounds present in the gaseous or liquid hydrocarbons to react with a cyanamide compoundv to form thiourea and isothiourea ethers.

(Cl. 26o-552) Thiourea has chemical properties which make it attractive for many industrial applications; but its high price has made its use prohibitive except when an -expensive material is justified.

Thiourea has been made by heating ammonium thiocyanate, but thismethod is quite expensive' because of low yields and the expense of ammonium thiocyanate. Thiourea has also been prepared from the reactionlfof basic suliides such as ammonium'sulilde on cyanamide and by the reaction of hydrogensulde on calcium cyanamide using refrigeration to maintain low temperatures.- These methods and others have failed to make thiourea available at a low price. l

This invention discloses a method of preparing thiourea oi high quality at a low cost. The

thiourea is prepared as a result of the sweetening of sour natural gas by a calcium cyanamide solution as described in applicants copending application, Serial No. 214,834 led June 20, 1938. The ,hydrogen sulde contained -in the natural gas reacts with the calcium. cyanamide solution to formfthiourea. 'I'he reaction between hydrogen suliide and calcium cyanamide is exothrmic and the solution becomes sufdciently warm to cause side reactions. This is undesirable and must be prevented. Previous patentsI have suggested the use of ice or other cooling methods. Refrigeration increases the cost of the operation and makes a more complicated plant.

In this invention no coolingis necessary because the volume of inert natural gas dilutes the hydrogen sulfide and at the same time carries o any heat of reaction as fast as it is formed.

Nitrogen or-other gases inert to the chemicals involved in the reaction would have a 'comparative effect when used as a diluent for the hydro- -gen sulde. "'Ihe mixture of gases represents the chief reasoni for the success of this process over others and isnovel to the art of manufacturing thiourea.

An object of the invention is to provide a process in which, if desired, the spent agent or agents employed to sweeten sour oils, d istillates or gases may be processed to secure a thiourea solution.

A further object of the invention is to provide -a. process in which, if desired, the spent agent or agents employed to sweeten sour oils, distillates or gases may beacidifled and then processed to secure thioureacrystals.

Other objects and advantages along with the foregoing will be apparent to those skilled in the art to which the present invention pertains from the disclosure thereof hereinafter set forth, and.

are attained by the invention described in detail y below.

now U. S. Patent 2,235,936.

In the accompanying-'drawing we have shown diagrammatically certain kinds of apparatus which may be used in carrying out the treatment, but it is to be. understood thatthe invention is in no sense restricted to those particular types of apparatus.

Figure 1 shows a diagrammatic view of sweetening process, i

Figure 2 showsa diagrammatic view of the process wherein the sweetening process is connected with apparatus to process the spent agent or agents so as to recover a thiourea solution,

Figure 3 shows a diagrammatic view of another modiiication'of the process wherein the sweetening process is-connected with .apparatus to process the spent agent or agents with an acid so as to recover thiourea crystals and a iiltrate.

Calciu`m cyanamide or any cyanamide -comthe T;

pound will remove mercaptans from hydrocarf bons'as well as removing the hydrogen sulfide. The cyanamide and mercaptan react to form isothiourea ethers'which are quite insoluble in the solvents present.

Referring more particularly to Figure 1, which constitutes a proposed showing of apparatus for the preferred modiiication of the process for the removalof hydrogen sulde from gases by the use of commercial calcium cyanamide, I rep' resents a mixing tank wherein calcium cyanamide from line 2 is mixed or dissolved in water from line 3. It is essential' that the temperature in the mixing tank be kept below25 C. throughout the mixing. From the mixing tank I, the suspension passes through the. lter l where it is ltered and the'i'lltrate containing the calcium cyanamide is fed continuously into the top of the scrubber tower 1 from storage tank 5 bymeans of pump 6. It is to be noted thatA sulphur, thiourea, ammonia or other amines may be added as a catalyst to the calcium cyanamide solution when the same is in the storage tank 5. 'I'he raw gas enters the scrubber tower 1 at the bottom thereof through the line 8 and the piu'iediprodleaves the bottom 'of the tower 'l through the line l0. This spent scrubber solution contains thiourea, calcium sulfhydrate and a precipitate of calciuni carbonate `formed from the calcium.

natural gas.

Referring now to Figure 2 which shows a modidesired and passed through both lines Il and I8.'

The spent scrubber solution passing through line I8 passes to filter I9 where the solution is filtered and thence to evaporator 20 where some of the liquid -is evaporated off. The steps under this process are carriedl out preferably under reduced pressure and the evaporation proceeds until the thiourea reaches concentration suitable for use in making synthetic resins and is stored in tank 2|. If the line Il is completely closed, by this method there is no recycling of the spent material, instead it is used as a raw material for the manufacture of resins or other purposes for which it is applicable. n

Referring to the process shown in Figure 3, the

lspent scrubber solution maypass from line I to line 22 or thesolution may be divided in any proportions desired between the other two lines, and passed to the mixer tank 23. Connecting into tank 23 is the line 24 which delivers a dilute sulphuric acid or any other acid to the tank and mixes the same with the spent scrubber solution to acidify the same and the whole is cooled. If desired, in place of the dilute sulphuric acid, the carbon dioxide from the flue gases may be used where such is available. Hydrogen sulfide is driven off from the spent scrubber solution and the residue goes to -theiilter 26. 'Ihe filtrate is evaporated in evaporator 21 from where the fluid passes to crystallizing tank 28. The solution then passes to filter 29 where the thiourea crystals are removed from the filter and the filtrate is pumped back to mixing tank I through pipe 30 where it dissolves more crude calcium cyanamide or if desired may be discarded.

This process of removing hydrogen sulde is continuous by any of the methods described. It may be a method of removing hydrogen sulde in which only enough fresh chemical for makeup is required, or it may be a method of removing hy- `alent or 76 pounds of thiourea which may beY cyanamide and carbon dioxide contained in most a bed of dry calcium cyanamide or is 'scrubbed with a solution or suspension of calcium cyanamide in water or other solvent in the conventional countercurrent type of scrubber. The theoretical reaction involved is illustrated in the n following chemical equation:

csCN, -i-ams =oa(sH). +Cs NH,), Calcium hydrogen calcium thioureo cyanamide sulilde `sulihydrate According to this equation, one weight equivalent, for instance 80 pounds, of calcium 'cyanamide should react with three weight equivalents or 102 pounds of hydrogen sulde to form as one of the products of the reaction one weight equivseparated as a valuable by-product. In practice?A it has been found that a much greater weight of vhydrogen sulfide is required to react with the@ same weight of calcium cyanamide which would indicate that the reaction is more complex than that indicated by the chemical equation as given.

If desired, it is not necessary to have the calcium cyanamide in solution with water but the same may be used in a dry state.` Dry granular calcium cyanamide may be packed in an upright cylindrical tank which should be equipped'wlth coils cooled by circulating water to maintain the temperature below 100 F. and the gas containing hydrogen sulde is passed upwardly through the tank. The gas contacts the calcium cyanamide and the hydrogen sulfide is absorbed rapidly with the process continuing until the ellluent gas shows traces of hydrogen sulfide when the flow of gas is I switched to another similar absorber while the spent calcium cyanamide in the first cylinder is extracted with solvents to remove the thiourea after which the absorber is cleaned and recharged with a fresh batch of calcium cyanamide and is drogen sulde from gas which yields a source of i thiourea for industrial purposes. It is to be understood that while sour gas has been usedto illustrate the apparatus shown in the drawing, similar setups could .be used for sweetening other sour hydrocarbons and it is not to be understood that the process is limited only to gas.

Itis not essential to have a complete plant as just described but a suspension of calcium cyanamide in a tower equipped with proper agitation affords an eilicient method of hydrogen sulfide removal, however, the recovery of thiourea is more diflicult. Calcium cyanamide, for instance, may be used dry, as a paste, or a suspension in a solvent such as water to remove hydrogen sulfide from hydrocarbons such as natural gas, coal gas,

ready fora new cycle of operation. In treating gasoline or kerosene to remove the sulphur compounds, this treatment may be applied by passing the vapors over a bed of calcium cyanamide or cyanamide.

` From the foregoingfit is believed that the steps and advantages of the process may be readily understood by those skilled in the art and it is manifest that changes may be made in the details disclosed without'departing from the spirit of the invention,as expressed in the claims. In' the appended claims, we mean the term hydrocarbons to generically define gasoline, kerosene, l

and other petroleum distillates and oils.

Having thus described our. invention, what we claim is:

1. The process of making thiourea which comprises treating hydrocarbon gas containing., hy-

drogen sulde present in the hydrocarbon gas normally as an impurity, with a solution of calcium cyanamide and water in a lscrubber tower and then taking the spent scrubber solution from the scrubber tower through a filter and evaporator to remove the thiourea therefrom.

2. 'I'he process of making thiourea which comdrogen sulfide present inthe hydrocarbon l normally as an impurity, with a solution of cal prises treating hydrocarbon -gas containing 13;/

, cium cyanamide and water in a 'scrubbertowerf neutralizing the spent scrubber solution with a r dilute acid, then filtering andevaporating' the residue and allowing thesame' 'toc remove the thiourea.

cimeli: n. Mums. EUGENE J..GATCHELL WILLIAM BRUCE -LERCH. 

